Investigators in the Laboratory of Drug Discovery Research and Development, DTP, DCT, NCI, recently discovered a series of novel dimeric polyhydroxylated naphthalene-tetrahydroisoquinoline alkaloids by bioassay guided fractionation of the leaves acquired from Ancistrocladus abbreviatus (Ancistrocladaceae), a vine found in the canopy of a tropical rain forest in Cameroon, using an in vitro screen against human immunodeficiency virus (HIV). The compound designated michellamine B (MB) completely protects human lymphoblastoid cells in vitro from the cytopathic effects of HIV types 1 and 2 at concentrations (EC50 ~20 fM) that were only moderately cytotoxic to uninfected cells (IC50 ~200 fM). Based upon these findings, MB was recently approved for continued preclinical evaluation as an anti-HIV agent by the Decision Network Committee. In support of this effort, we have developed a sensitive and specific assay to quantitate the compound in biological fluids. The method involves solvent denaturation to isolate the compound from endogenous macromolecules followed by high performance liquid chromatography with fluorescence detection. The assay has been extensively vali-dated and utilized to characterize the aqueous solution stability of MB and its pharmacokinetic behavior in the mouse and dog.